Conventionally, there has been carried out a collection of a particulate matter (hereinafter, referred to as PM) in an exhaust gas by using a particulate filter (hereinafter, referred to as filter), for purifying the exhaust gas, in an internal combustion engine, particularly in a diesel engine. In this case, if the PM collected by the filter exceeds a predetermined amount, a distribution resistance within the filter is increased so as to cause a reduction of an engine output. Accordingly, there has been carried out a recovery of a PM collecting capacity of the filter (a regeneration of the filter) by removing the PM deposited on the filter.
As one example of this kind of regeneration system, there is a chemical reaction type regeneration system. The chemical reaction type regeneration system is structured such that the PM is oxidized and removed by oxidizing a nitrogen monoxide (NO) in the exhaust gas into an unstable nitrogen dioxide (NO2) by an oxidation catalyst existing in an upstream side of a filter in an exhaust path of an engine, and using an oxygen (O) discharged at a time when NO2 comes back to NO. It is possible to regenerate the filter during an engine drive by utilizing an oxidation action of the oxidation catalyst mentioned above.
In this case, in the chemical reaction type regeneration system, the chemical reaction is carried out only in the case where a temperature of the exhaust gas is equal to or higher than a regenerable temperature (for example, about 300° C.). In other words, if a state in which the exhaust gas temperature is lower than the regenerable temperature continues, the PM is deposited in a large quantity on the filter. As a result, the filter is clogged. Accordingly, it is necessary to make the exhaust gas temperature equal to or higher than the regenerable temperature in the case where the PM deposition amount reaches a predetermined amount.
In this regard, in patent document 1, there is disclosed a matter that an electrothermal type heater is provided in an upstream side of a filter with oxidation catalyst in an exhaust path of an engine, and an exhaust gas temperature conducted to the filter with oxidation catalyst is raised on the basis of a heater heating.    Patent Document 1: Japanese Unexamined Patent Publication No. 2001-280121